1. Field of Invention
The invention relates to instruments used by electricians and electronic technicians for indicating the presence or absence of continuity, or the presence or absence of an electrical potential in an electric circuit. An example of a continuity-voltage indicating device is found in my U.S. Pat. No. 4,066,953, which issued on Jan. 3, 1978. An example of a continuity tester is the usual ohm meter, and examples of voltage-indicating devices are the usual neon tester and voltmeter.
2. Description of Prior Art
The ohm meter may most simply consist of a battery in series with a current-reading meter and which is connected in series with the electrical path whose continuity is to be checked. Another commonly used continuity tester may consist simply of a battery in series with a lamp bulb where a quantitative resistance determination is not required.
The common voltage-sensing instruments above noted (neon tester and voltmeter) are not usable by themselves and without further implementation for sensing continuity in electrical circuits, and similarly, the continuity testers in common use by electricians and technicians are not usable by themselves and without further implementation for determining the presence of an electrical potential. These two types of instruments are perhaps the most universally used by electricians and technicians, and a single compact, portable and easily carried unit performing both of these diverse functions would be most useful.
Certain more sophisticated instruments using solidstate amplifiers have been designed for specific applications, principally low resistance sensing, see U.S. Pat. Nos. 3,283,244 and 3,328,684; British Pat. No. 910,045/1962; and French Pat. No. 1,236,403/1960. These specialized testers have been designed for sensing and indicating very low resistance from just a few ohms to a few thousand ohms; have no use as a continuity tester in circuits having a much higher resistance, e.g., up to 1 megohm or more; and cannot be used for any practical voltage sensing, at least in the higher ranges of voltage normally encountered by the electrician or technician.
The instrument of the present invention affords certain advantages over the instrument disclosed in my U.S. Pat. No. 4,066,953 in its ability to distinguish AC and DC voltages and its assurance against possible shock hazard as might be caused by accidental breakdown or shortage of insulation or components affording normal isolation in the circuitry of the instrument.